Transducers are used in a wide variety of electronic applications. One type of transducer is known as a piezoelectric transducer. A piezoelectric transducer comprises a piezoelectric material disposed between electrodes. The application of a time-varying electrical signal will cause a mechanical vibration across the transducer; and the application of a time-varying mechanical signal will cause a time-varying electrical signal to be generated by the piezoelectric material of the transducer. One type of piezoelectric transducer may be based on bulk acoustic wave (BAW) resonators and film bulk acoustic resonators (FBARs). As is known, certain FBARs and BAW devices over a cavity in a substrate, or otherwise suspending at least a portion of the device will cause the device to flex in a time varying manner. Such transducers are often referred to as membranes.
Among other applications, piezoelectric transducers may be used to transmit or receive mechanical and electrical signals. These signals may be the transduction of acoustic signals, for example, and the transducers may be functioning as microphones (mics) and speakers and the detection or emission of ultrasonic waves. As the need to reduce the size of many components continues, the demand for reduced-size transducers continues to increase as well. This has lead to comparatively small transducers, which may be micromachined according to technologies such as micro-electromechanical systems (MEMS) technology, such as described in the related applications.
The materials that comprise the membrane often have properties that are temperature dependent. Notably, the piezoelectric materials, electrodes and contacts are temperature dependent. For example, FBAR devices in which the material of the piezoelectric element is aluminum nitride (AlN) and the material of the electrodes is molybdenum (Mo), have a resonance frequency that depends on temperature, which has an impact on device performance. Moreover, in certain applications, membrane-based devices will be commonly subjected to increased temperatures relative to the ideal temperature or design point, while in other applications the membranes are subjected to reduced temperatures relative to the ideal temperature or design point.
What is needed, therefore, is an apparatus that overcomes at least the drawbacks of known transducers discussed above.